1. Technical Field
The present disclosure relates to a toner and a method of manufacturing toner.
2. Description of the Background
To meet recent demand for high image quality, toner is required to be much smaller. It is technically difficult to produce small-sized toner particles by typical kneading and pulverizing processes. Disadvantageously, toner particles obtained through such processes have irregular shapes and a wide particle size distribution and require a large amount of energy when being fixed on paper. When raw materials include a binder resin and a release agent such as a wax, it is likely that the kneaded mixture of the raw materials is pulverized from each interface between the binder resin and the release agent. As a result, the release agent is likely to exist at the surfaces of resulting toner particles. The release agent existing at the surface of toner particle helps releasing of the toner particle from a fixing member, but disadvantageously contaminates carrier particles, photoreceptor, or blade members.
On the other hand, toner manufacturing methods using polymerization processes have been also proposed. Generally, it is relatively easy for polymerization processes to produce small-sized toner particles with a narrow particle size distribution. It is also possible for polymerization processes to make a release agent encapsulated in resulting toner particles. For example, Japanese Patent Application Publication Nos. 63-282752 and 06-250439 each proposes an emulsion polymerization aggregation method. As another example, Japanese Patent Application Publication Nos. 2000-275907 and 2001-305797 each proposes an emulsion polymerization aggregation method.
To meet another demand for energy saving, toner is required to be fixable at much lower temperatures so as to reduce the electric power needed for warming up an image forming apparatus.
One approach for reducing fixable temperature of toner involves reducing the softening point of binder resin. However, such a low-softening-point resin portion in toner may be adhered to a fixing member and undesirably retransferred onto a next sheet of paper. This phenomenon is hereinafter referred to as hot offset. Reducing the softening point of binder resin may also reduce heat resistance of toner. As a result, the toner particles easily fused to each other (hereinafter “toner blocking”) when stored in high-temperature conditions. Such toner particles may also contaminate a developing device, carrier particles, and photoreceptor.
Japanese Patent Application Publication No. 11-133665 describes a toner having a specific sphericity including an urethane-modified polyester-based binder resin. Japanese Patent Application Publication Nos. 2002-287400 and 2002-351143 each describes a small-sized toner. Each of these publications describes a toner manufacturing method in which a polyester prepolymer having an isocyanate group is addition-polymerized with an amine in an organic solvent and an aqueous medium to prepare a polymer, followed by removal of the organic solvent. Japanese Patent Application Publication No. 2005-77776 further describes in detail the removal process of the organic solvent.
Japanese Patent Application Publication Nos. 2001-242663 and 2005-156586 each describes a polymerization toner.
Japanese Patent Application Publication No. 2010-061071 describes a toner in which the difference (Tb−Ta) between the softening point Ta of the binder resin and the softening point Tb of the toner is controlled. It is described therein that the control of (Tb−Ta) is for adjusting low-temperature fixability and heat-resistant storage stability.